1. Field of the Invention
The present invention relates to a surface-mount crystal oscillator, and more particularly, to a sheet substrate for use in assembling surface-mount crystal oscillators, and to a method of manufacturing surface-mount crystal oscillators using the sheet substrate.
2. Description of the Related Art
Surface-mount quartz crystal oscillators, which have a surface-mount container that contains a quartz crystal unit and an oscillator circuit connected to the crystal unit, are widely used as reference sources for the frequency or time in portable electronic devices because of their compact size and light weight. Among these surface-mount crystal oscillators, particularly widely used for portable telephones and the like are surface-mount temperature-compensated crystal oscillators which compensate the oscillation frequency for variations due to a varying temperature in the ambient.
FIG. 1 is a partially broken front view illustrating an exemplary configuration of a conventional surface-mount temperature-compensated crystal oscillator. This temperature-compensated crystal oscillator has container body 1 substantially in rectangular solid which is made, for example, of laminated ceramic and formed with a recess. Container body 1 contains IC (integrated circuit) chip 2 and quartz crystal blank 3. Lid 4 covers the recess, for example, by seam welding to enclose IC chip 2 and crystal blank 3 in the recess. Integrated in IC chip 2 are an oscillator circuit connected to crystal blank 3, and a temperature compensating mechanism for compensating the oscillation frequency for variations caused by a varying temperature in the ambient. IC chip 2 is secured on the bottom of the recess in container body 1 by facedown bonding using bumps or the like. As illustrated in FIG. 2, crystal blank 3 is, for example, a substantially rectangular AT-cut crystal blank which is formed with excitation electrodes 5 on both main surfaces, respectively. Lead-out electrodes 6 extend from respective excitation electrodes 5 to both corners on one side of crystal blank 3. Crystal blank 3 is held in the recess by securing the both corners on the one side to a step formed in the recess by conductive adhesive 7 or the like. In this way, lead-out electrodes 6 are electrically connected to IC chip 2 through a circuit pattern, not shown, or the like formed in the recess.
Generally, container body 1 is provided with mount terminals 8 at four corners on the bottom face thereof for use in surface-mounting the crystal oscillator on a circuit board or the like. Mount terminals 8 are electrically connected to IC chip 2 through via-holes or the like formed through container body 1.
A pair of opposing side faces of container body 1 are formed with data write terminals 9a electrically connected to a temperature compensating mechanism of IC chip 2 for use in writing data for temperature compensation into the temperature compensating mechanism. In addition, another pair of opposing side faces of container body 1 are formed with crystal measurement terminals 9b electrically connected to lead-out electrodes 6 of crystal blank 3 for confirming the electric characteristic of the crystal unit itself which is comprised of crystal blank 3. Since the frequency-temperature characteristic differs from one crystal blank to another, the temperature dependency of the oscillation frequency is measured for each crystal oscillator to write temperature compensation data corresponding to the measured characteristic into the temperature compensating mechanism through data write terminals 9a prior to the shipment of the crystal oscillator.
In recent years, a reduction in size or miniaturization has been increasingly required for the surface-mount temperature-compensated crystal oscillators, and there is an ongoing need for a crystal oscillator which has the dimensions of 3.2 mmxc3x972.5 mm and a thickness (height) of 1.0 mm, by way of example. Such advancement in miniaturization gives rise to a problem that no margin can be ensured to form data write terminals 9a and crystal measuring terminals 9b on the side faces of container body 1. Particularly, it is difficult to form these terminals on the shorter ones of the sides which define the geometry of container body 1. While a reduction in size can be contemplated for data write terminals 9a and crystal measuring terminal 9b themselves, these terminals must be provided with minimal areas which are determined from the relationship with probes from a measuring device used for measuring the characteristic of crystal blank 3 or writing temperature compensation data. In addition, reduced spacings between these terminals and mount terminals 8 would cause short-circuiting of both through soldering scobs or the like which can be produced upon mounting to an external circuit board.
Furthermore, although data write terminals 9a and crystal measuring terminals 9b are required only when the crystal oscillator is manufactured and are not basically needed after the manufacturing, they are left on the crystal oscillator even after the shipment, thereby possibly causing troubles after a consumer has mounted the crystal oscillator on a circuit board or the like. The troubles occur with a higher probability as a larger number of terminals are formed on the side faces of the container body.
It is an object of the present invention to provide a sheet substrate which is used for the manufacturing of a surface-mount crystal oscillator and which is suitable for a reduction in size of the crystal oscillator.
It is another object of the present invention to provide a method of manufacturing surface-mount crystal oscillators which are suitable for a reduction in size.
The object of the present invention is achieved by a sheet substrate for collectively fabricating a plurality of container bodies each for use in a surface-mount crystal oscillator in a manner that the container bodies are integrally connected to each other, wherein each of the container bodies is capable of accommodating at least one IC chip, and has a bottom face formed with a plurality of mount terminals and a top face which is capable of forming a crystal unit thereto. Each of the container bodies on the sheet substrate includes a conductive path extending from the container body to an adjacent container body and connected to a mount terminal of the adjacent container body, and a chip carrying terminal connected to one end of the conductive path for use in electric connection with the IC chip.
The other object of the present invention is achieved by a method of manufacturing surface-mount crystal oscillators using the sheet substrate according to the present invention. The method includes detecting a characteristic or writing data for each container body using the mount terminal of another container body adjacent to the container body, and subsequently dividing the sheet substrate into individual crystal oscillators.
In the present invention, since an IC chip mounted in a certain container body in the sheet substrate can be electrically connected using the mount terminal of a container body adjacent to this container body, the mount terminal of the adjacent container body can be utilized for writing data into the IC chip or for measuring the characteristic of a crystal blank in the container body. Since electric connections with adjacent container bodies are broken after the sheet substrate is divided into individual crystal oscillators, as a matter of course, the conductive paths to the adjacent container bodies will not adversely affect the operation of the resulting crystal oscillators. According to the present invention, a reduction in size is promoted for the surface-mount crystal oscillator because the container body need not be additionally provided with such terminals that are required only during the manufacturing in a factory, for example, terminals for writing data into the IC chip or measuring the characteristic of the crystal blank.